806 research outputs found
Analysis of patterns formed by two-component diffusion limited aggregation
We consider diffusion limited aggregation of particles of two different
kinds. It is assumed that a particle of one kind may adhere only to another
particle of the same kind. The particles aggregate on a linear substrate which
consists of periodically or randomly placed particles of different kinds. We
analyze the influence of initial patterns on the structure of growing clusters.
It is shown that at small distances from the substrate, the cluster structures
repeat initial patterns. However, starting from a critical distance the initial
periodicity is abruptly lost, and the particle distribution tends to a random
one. An approach describing the evolution of the number of branches is
proposed. Our calculations show that the initial patter can be detected only at
the distance which is not larger than approximately one and a half of the
characteristic pattern size.Comment: Accepted for publication in Physical Review
The effects of various household cleaning methods on DNA persistence on mugs and knives
© 2019 Elsevier B.V. With the prevalence of forensic science in popular media, offenders are becoming more forensically aware and can employ precautionary methods, such as cleaning used items or rubbing away fingermarks, to reduce their traces left at a crime scene. This study examined the effects of various cleaning methods on DNA persistence on commonly encountered casework exhibits, specifically knives and mugs. Aliquots of acellular DNA were added to the knife handles or mug rims, allowed to dry, and then the substrates were either sampled directly or were cleaned and then sampled. The plastic- and wood-handled knives were cleaned with a cloth in a sink of water, diluted dish washing liquid or diluted household bleach, whereas the ceramic, glass and steel mugs were cleaned with a dry or wet cloth, or by wiping with a cloth after applying a cleaning product (dish washing liquid or household bleach spray) directly into the mug and then rinsing it with water. DNA samples were collected with wet and dry swabs, in triplicate, and extracted and quantified. In both experiments, DNA was not detected on items after cleaning with dish washing liquid or household bleach, irrespective of the differences in amounts of DNA initially deposited, substrates, and cleaning methods. Even without a cleaning product, rubbing with a dry cloth decreased DNA recovery from the mugs, regardless of the mug substrate. These results contribute to our understanding of the impact of various cleaning methods on DNA recovery at the crime scene and will help inform DNA recovery strategies
Dynamic scaling approach to study time series fluctuations
We propose a new approach for properly analyzing stochastic time series by
mapping the dynamics of time series fluctuations onto a suitable nonequilibrium
surface-growth problem. In this framework, the fluctuation sampling time
interval plays the role of time variable, whereas the physical time is treated
as the analog of spatial variable. In this way we found that the fluctuations
of many real-world time series satisfy the analog of the Family-Viscek dynamic
scaling ansatz. This finding permits to use the powerful tools of kinetic
roughening theory to classify, model, and forecast the fluctuations of
real-world time series.Comment: 25 pages, 7 figures, 1 tabl
Multifractal Dimensions for Branched Growth
A recently proposed theory for diffusion-limited aggregation (DLA), which
models this system as a random branched growth process, is reviewed. Like DLA,
this process is stochastic, and ensemble averaging is needed in order to define
multifractal dimensions. In an earlier work [T. C. Halsey and M. Leibig, Phys.
Rev. A46, 7793 (1992)], annealed average dimensions were computed for this
model. In this paper, we compute the quenched average dimensions, which are
expected to apply to typical members of the ensemble. We develop a perturbative
expansion for the average of the logarithm of the multifractal partition
function; the leading and sub-leading divergent terms in this expansion are
then resummed to all orders. The result is that in the limit where the number
of particles n -> \infty, the quenched and annealed dimensions are {\it
identical}; however, the attainment of this limit requires enormous values of
n. At smaller, more realistic values of n, the apparent quenched dimensions
differ from the annealed dimensions. We interpret these results to mean that
while multifractality as an ensemble property of random branched growth (and
hence of DLA) is quite robust, it subtly fails for typical members of the
ensemble.Comment: 82 pages, 24 included figures in 16 files, 1 included tabl
No self-similar aggregates with sedimentation
Two-dimensional cluster-cluster aggregation is studied when clusters move
both diffusively and sediment with a size dependent velocity. Sedimentation
breaks the rotational symmetry and the ensuing clusters are not self-similar
fractals: the mean cluster width perpendicular to the field direction grows
faster than the height. The mean width exhibits power-law scaling with respect
to the cluster size, ~ s^{l_x}, l_x = 0.61 +- 0.01, but the mean height
does not. The clusters tend to become elongated in the sedimentation direction
and the ratio of the single particle sedimentation velocity to single particle
diffusivity controls the degree of orientation. These results are obtained
using a simulation method, which becomes the more efficient the larger the
moving clusters are.Comment: 10 pages, 10 figure
Diffusion-Limited Aggregation Processes with 3-Particle Elementary Reactions
A diffusion-limited aggregation process, in which clusters coalesce by means
of 3-particle reaction, A+A+A->A, is investigated. In one dimension we give a
heuristic argument that predicts logarithmic corrections to the mean-field
asymptotic behavior for the concentration of clusters of mass at time ,
, for . The total
concentration of clusters, , decays as at . We also investigate the problem with a localized steady source of
monomers and find that the steady-state concentration scales as
, , and , respectively,
for the spatial dimension equal to 1, 2, and 3. The total number of
clusters, , grows with time as , , and
for = 1, 2, and 3. Furthermore, in three dimensions we
obtain an asymptotic solution for the steady state cluster-mass distribution:
, with the scaling function
and the scaling variable .Comment: 12 pages, plain Te
Interfaces with a single growth inhomogeneity and anchored boundaries
The dynamics of a one dimensional growth model involving attachment and
detachment of particles is studied in the presence of a localized growth
inhomogeneity along with anchored boundary conditions. At large times, the
latter enforce an equilibrium stationary regime which allows for an exact
calculation of roughening exponents. The stochastic evolution is related to a
spin Hamiltonian whose spectrum gap embodies the dynamic scaling exponent of
late stages. For vanishing gaps the interface can exhibit a slow morphological
transition followed by a change of scaling regimes which are studied
numerically. Instead, a faceting dynamics arises for gapful situations.Comment: REVTeX, 11 pages, 9 Postscript figure
Nontrivial Polydispersity Exponents in Aggregation Models
We consider the scaling solutions of Smoluchowski's equation of irreversible
aggregation, for a non gelling collision kernel. The scaling mass distribution
f(s) diverges as s^{-tau} when s->0. tau is non trivial and could, until now,
only be computed by numerical simulations. We develop here new general methods
to obtain exact bounds and good approximations of . For the specific
kernel KdD(x,y)=(x^{1/D}+y^{1/D})^d, describing a mean-field model of particles
moving in d dimensions and aggregating with conservation of ``mass'' s=R^D (R
is the particle radius), perturbative and nonperturbative expansions are
derived.
For a general kernel, we find exact inequalities for tau and develop a
variational approximation which is used to carry out the first systematic study
of tau(d,D) for KdD. The agreement is excellent both with the expansions we
derived and with existing numerical values. Finally, we discuss a possible
application to 2d decaying turbulence.Comment: 16 pages (multicol.sty), 6 eps figures (uses epsfig), Minor
corrections. Notations improved, as published in Phys. Rev. E 55, 546
Monitoring birds, reptiles and butterflies in the St Katherine Protectorate, Egypt
Fifty-two bird species were recorded during transect and point count surveys of wadis in the St Katherine Protectorate in the mountainous southern region of the Sinai, Egypt. Two species are new to Egypt: Rock Nuthatch (Sitta neumeyer) and Rock Sparrow (Petronia petronia). There were several other notable species: migrants such as Arabian Warbler (Sylvia leucomelaena) and Upcher’s warbler (Hippolais languida); and residents such as Verreaux’s Eagle (Aquila verreauxi), Hume’s Tawny Owl (Strix butleri) and Striated Scops Owl (Otus brucei).Estimates of bird density and descriptions of each wadi are given. Species diversity of wadis within the Ring dyke geological feature bounding the central mountain plateau was not significantly different from wadis outside. Species composition and numbers of individuals varied according to the distribution of water sources, natural trees and Bedouin gardens especially in fruit. These features appear to be particularly important as staging posts for migrants. Numbers ofsome birds increased around tourist areas. Observations of seven species of reptile and ten species of butterfly including endemics arealso presented. Recorded numbers of all groups depended heavily on the time of day
A pseudo-spectral approach to inverse problems in interface dynamics
An improved scheme for computing coupling parameters of the
Kardar-Parisi-Zhang equation from a collection of successive interface
profiles, is presented. The approach hinges on a spectral representation of
this equation. An appropriate discretization based on a Fourier representation,
is discussed as a by-product of the above scheme. Our method is first tested on
profiles generated by a one-dimensional Kardar-Parisi-Zhang equation where it
is shown to reproduce the input parameters very accurately. When applied to
microscopic models of growth, it provides the values of the coupling parameters
associated with the corresponding continuum equations. This technique favorably
compares with previous methods based on real space schemes.Comment: 12 pages, 9 figures, revtex 3.0 with epsf style, to appear in Phys.
Rev.
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